The destruction of Syria's chemical weapons stockpile has been completed, Barack Obama has said.

The US President welcomed the development, but said Washington would seek to ensure Damascus fulfils all its commitments.

"Today we mark an important achievement in our ongoing effort to counter the spread of weapons of mass destruction by eliminating Syria's declared chemical weapons stockpile," he said.

He added that the destruction, carried out aboard a US Navy ship on the Mediterranean Sea, sent "a clear message that the use of these abhorrent weapons has consequences and will not be tolerated by the international community".

Image Caption:Syria's devastating war has left more than 170,000 people dead

President Bashar al Assad's regime agreed to an international plan to destroy its stockpile, after a global outcry over deadly chemical attacks in a Damascus suburb last year that may have killed as many as 1,400 people.

"Going forward, we will watch closely to see that Syria fulfills its commitment to destroy its remaining declared chemical weapons production facilities," Mr Obama said.

US Secretary of State John Kerry insisted "much more work must be done" but described it as "a milestone in our unrelenting work to ensure the end of the Assad regime's deadly chemical arsenal".

"The United States will continue to provide political, financial and other support to the moderate opposition because we are committed to help those who seek the right of all Syrians to choose a future of peace and oppose the violent extremists who exploit the chaos and ruin that Assad has brought to Syria," he said in a statement.

Image Caption:More than two million Syrian refugees have fled the three-year conflict

With no country willing to accept shipments of Syria's most deadly chemical agents, the United States opted to destroy the substances at sea using two "portable" hydrolysis units.

Defence Secretary Chuck Hagel called the captain of the MV Cape Ray earlier in the day to congratulate the crew on "their unprecedented work of neutralising, at sea, the most dangerous chemicals in Syria's declared stockpile".

The process involved mixing the chemicals in sealed containers with thousands of gallons of hot water and sodium hydroxide or other "reagents" that help break down their toxicity.

Officials say none of the chemicals or waste will be dumped at sea.

More than 170,000 people are estimated to have died in Syria's civil war, which began in March 2011.